1. Field of the Invention
The present invention relates to processes for deforming metal tubes. More specifically, the invention relates to a process for cold forming an end of a pipe to provide a reinforced portion.
2. Description of the Prior Art
In the automotive industry, vehicles are often fitted with a hitch assembly to which a trailer may be attached. Such assembly usually includes a hitch receiver tube and a hitch bar slidably engaged within same. The hitch bar includes a ball onto which the trailer is attached. The hitch receiver tube is mounted on the vehicle frame by a suitable means such as brackets and the like and is normally provided at its terminal end (i.e. the end into which the hitch bar inserted) with a reinforcing collar. Although such collar increases the strength of the end of the tube, various problems have been found with this structure. For example, the reinforcing collar must be welded on the bar thereby reducing its aesthetic qualities. Further, since a complete seal is not possible, the accumulation of water and salt within any spaces accelerates the corrosion of the entire structure.
Various solutions have been proposed to address the above issue. One example is described by Marquardt in U.S. Pat. No. 5,203,194. Marquardt teaches a process for reinforcing the terminal end of a hitch receiver tube wherein the wall thickness at the end is increased in a forming process. In this reference, the tube is heated to approximately 1800xc2x0 F. and then placed within a die cavity having a flared region adjacent to the tube""s terminal end. A mandrel is then inserted into the die and used to apply pressure to the tube""s terminal end. This forces the tube material into the flared region thereby increasing the thickness of the tube at its end. This reference essentially teaches a forging process.
Although this reference provides a hitch receiver tube with the required reinforcement and which may overcome the problems mentioned above, there are still some deficiencies in the disclosed process. The main disadvantage with the Marquardt process lies in the requirement for heating the tube prior to the forming stage. As will be appreciated, such heating greatly increases the time a cost of producing each tube. Further, the heating of the tube results in carburization of its outer surface. The deposits resulting from the carburization must then be removed thereby further increasing the tube production time. In addition, the heating of the tube deteriorates its structural integrity thereby resulting in weakness.
Other references dealing with tube end forming processes include U.S. Pat. Nos. 4,845,972 and 4,213,322. However, these references all teach the heating of the tube prior to forming.
Thus, there is a need for a receiver tube forming process that overcomes the deficiencies in the known methods.
Thus, the present invention provides, in one embodiment, a process for reinforcing the end of a metal tube having inner and outer surfaces and first and second ends, the process comprising the steps of:
a) providing a die having first and second ends and defining a cavity conforming to the outer surface of the tube, the cavity having a recess at the first end that is wider than the tube;
b) placing the tube in the die cavity such wherein the tube first end extends out of the die cavity beyond the die first end;
c) providing a means for preventing movement of the tube longitudinally with respect to the die cavity;
d) providing a mandrel having a first portion adapted to fit within the tube through the tube first end, the mandrel also having second portion with a tube deforming surface adapted to impinge upon the tube first end;
e) inserting the mandrel first portion into the first end of the tube until the tube deforming surface contacts the first end of the tube;
f) advancing the mandrel under pressure thereby causing deformation of the first end of the tube and folding of same into the recess of the die cavity.
The invention also provides a tube having a first end wherein the first end includes a radially extending reinforced portion comprising a section of the tube folded upon itself.